Evaluation of dew point corrosion in acid atmosphere by wire beam electrode

In this article, wire beam electrode (WBE) was used to evaluate the corrosion behavior of ND steel in environmental acid atmosphere with different partial pressure of CO₂. Meanwhile, corrosion products and surface morphology analysis also used to support this research. The results showed that the corrosion behavior began from the edge of droplet in dew point corrosion, and gradually spread to the center of it. The spread speed would increasing with CO₂ partial pressure enhance, which was 24h in 5% CO₂ and 4h in 50% CO₂. Corrosion current density in the edge of droplet can form the "cathode-anode-cathode ring" structure, and disappears gradually as the corrosion time was going. Corrosion morphology observation results showed three ring shapes region and different elemental composition of different corrosion products, which is correspondence with the "cathode-anodWe-cathode ring" structure measured in WBE experiments. The results showed that the reaction gradually transferred to the uniform corrosion on electrode surface when the dew point corrosion reaction reaching the late stage. It comes from the dissolution, diffusion and reaction of gaseous corrosion medium of CO₂ and O₂.